You can use CSS hover in combination with an image background.
CSS
.image
{
background:url(images/back.png);
height:100px;
width:100px;
display: block;
float:left;
}
.image a {
display: none;
}
.image a:hover {
display: block;
}
HTML
<div class="image"><a href="#">Text you want on mouseover</a></div>